I have to echo John’s points about Firewire and external hard drives. There are no Firewire peripheral devices on the shelf – or otherwise easily available any more. And with the various generations of Thunderbolt to use instead, why would there be?
I edit all my work onto external TB2 hard drives, which are backed up onto external RAID arrays. It’s probably more redundancy than most people want or need, but it gives me peace of mind. And it also provides the freedom to change my editing machine whenever I want. So, I can switch from the MacBook Pro I use today (perfectly suitable for all HD editing I do on Premiere Pro these days) to an iMac or MacPro down the road. The only thing that lives on my internal drives is the OS and the software programs I use to work with.